Human T lymphocyte/monocyte interaction in response to lectin: kinetics of entry into the S-phase.

PHA-mediated mitogenesis of human peripheral blood T lymphocytes was studied by using highly purified cell populations. The kinetics of human, mature T cell [3H]-Tdr incorporation were examined with respect to those elements necessary and sufficient for the progression of the activated T cell into the S-phase of the cell cycle. These experiments indicated that although a lectin may independently initiate morphologic T cell blastogenesis, this event is not associated with significant progression through the G1 phase of the cell cycle. This blastogenic response is associated with the subsequent T cell receptivity to monocyte-initiated cell cycle progression, and the effect of monocytes can be substituted by partially purified Interleukin 1 (IL-1). Progression of a lectin exposed T cell into the S-phase of the cell cycle could also be achieved by exposing the activated T cell to partially purified Interleukin 2 (IL-2). Given the prior demonstrations that IL-1 functions to induce the T cell-dependent production of the IL-2, it appears that IL-2 is the requisite signal necessary for the activated human lymphocyte to actually progress through the prereplicative phase of the cycle into the S-phase.